I have adopted a 2 year old miniature purebred dachshund from a person who rescues dogs from abusive puppy mills.
Molly came housebroken but since she has been here now for 2 months, she has begun using my spare room to relieve herself. She is ruining the new carpet.
I am afraid that as I have 3 other dogs and a cat, she will have them relieving themselves in the house as well.
Any advise is helpful!!

Hi hisbride...
Have you tried any training techniques so far.
Being in a new home after being abused can be a very emotional time for a dog.
Even if they do behave perfectly when they first arrive they can fall back into old habits.
Try just re-training her as you would a puppy, take her outside when you catch her and tell her 'no' but don't get angry at her.

Being from a puppy mill she wouldn't have the had the best of care and treatment so scolding her at this time is probably not going to be the best idea.
It can take a long time for a dog to bond with you and until then you are just going to have to make sure you let her outside at regular intervals and give her lots of praise when she goes outside.

Good on you for adopting :)